Understanding WCAG 2.0

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Live Audio-only:
Understanding SC 1.2.9

1.2.9 Live Audio-only: [begin delete]A [end delete][begin add]An alternative for time-based media[end add][begin delete]text alternative[end delete] that presents equivalent information for live audio-only content is provided. (Level AAA)

Intent of this Success Criterion

The intent of this Success Criterion is to make information conveyed by live audio, such as video conferencing, live speeches and radio Webcasts, accessible through the use of a text alternative. A live text caption service will enable live audio to be accessible to people who are Deaf or hard of hearing, or who cannot otherwise hear the audio. Such services use a trained human operator who listens in to what is being said and uses a special keyboard to enter the text with only a small delay. They are able to capture a live event with a high degree of fidelity, and also to insert notes on any non spoken audio which is essential to understanding the event. A transcript is sometimes a possibility if the live audio is following a set script; but a live caption service is preferred because it plays out at the same pace as the audio itself, and can adapt to any deviations from the script that might occur.

Using untrained operators, or providing a transcript which differs markedly from what actually happens would not be considered meeting this Success Criterion.

Examples of Success Criterion 1.2.9

Related Resources

Resources are for information purposes only, no endorsement implied.

Techniques and Failures for Success Criterion 1.2.9 - Live Audio-only

Each numbered item in this section represents a technique or combination of techniques that the WCAG Working Group deems sufficient for meeting this Success Criterion. The techniques listed only satisfy the Success Criterion if all of the WCAG 2.0 conformance requirements have been met.

Additional Techniques (Advisory) for 1.2.9

Although not required for conformance, the following additional techniques should be considered in order to make content more accessible. Not all techniques can be used or would be effective in all situations.

  • Using metadata to associate text transcriptions with audio-only content (future link)

    Example: Providing, in metadata, URI(s) that point to several text transcripts (English, French, Dutch) of an audio file.

Common Failures for SC 1.2.9

The following are common mistakes that are considered failures of Success Criterion 1.2.9 by the WCAG Working Group.

(No failures currently documented)

Key Terms

[begin add]alternative for time-based media[end add][begin delete]full text alternative for synchronized media including any interaction[end delete]

document including correctly sequenced text descriptions of [begin delete]all visual settings, actions, speakers, and non-speech sounds, and transcript of all dialogue combined with a means of achieving any outcomes that are achieved using interaction (if any) during the synchronized media[end delete][begin add]time-based visual and auditory information and providing a means for achieving the outcomes of any time-based interaction [end add]

Note: A screenplay used to create the synchronized media content would meet this definition only if it was corrected to accurately represent the final synchronized media after editing.


a time-based presentation that contains only audio (no video and no interaction)


information captured from a real-world event and transmitted to the receiver with no more than a broadcast delay

Note 1: A broadcast delay is a short (usually automated) delay, for example used in order to give the broadcaster time to queue or censor the audio (or video) feed, but not sufficient to allow significant editing.

Note 2: If information is completely computer generated, it is not live.

text alternative

[begin delete]programmatically determined [end delete]Text that is [begin delete]used in place of[end delete][begin add]programmatically associated with[end add] non-text content[begin delete], or text that is used in addition to non-text content and referred to from the programmatically determined text[end delete][begin add] or referred to from text that is programmatically associated with non-text content. Programmatically associated text is text whose location can be programatically determined from the non-text content.[end add]

Example: An image of a chart is described in text in the paragraph after the chart. The short text alternative for the chart indicates that a description follows.

[begin add]

Note: Refer to Understanding Text Alternatives for more information.

[end add]